Optical fibers are used to transmit information over long distances, at the speed of light in glass. In order to achieve successfully this mission, optical fibers and the corresponding optical waveguide structures must be able to resist the potential alterations that may occur during the operational period of the fibers.
Moreover, deployment of optical fibers has shown a tremendous increase in the context of FTTx business (such as Fiber To The Home (FTTH), Fiber To The Curb (FTTC), . . . ). In this context, a specialty cable, filled with loose fiber modules that are designed to have low friction properties, is used as the core of the operation. Window-cuts can be made at multiple points along the cable length, so as to allow individual fiber modules to be cut and pulled back to one of those earlier window-cuts. These fiber modules can then be pushed or blown though separate micro-ducts to reach a termination or distribution point (typically on the customer premises).
It is important that such fiber modules have the flexibility to be pushed, pulled, bent, branched, and handled in ways that allow easy manipulation for installation, without reductions in loss or damage to the fiber core.
Patent document WO 2006/136558 discloses an optical fiber cable comprising: a protective sheath having an inner surface defining a cavity, one or more micro-cables or micro-tubes running inside the cavity, each micro-cable having an outer jacket, characterized in that the cross-sectional area of the micro-cables and micro-tubes is less than 75% of the cross-sectional area of the cavity, and in that the outer jacket of a micro-cable or of a micro-tube is formed of a material having a dynamic coefficient of friction that, when measured according to test A, is less than or equal to 0.2 and having a Shore hardness greater than 65. This patent document describes parallel modules made of a mixture of polycarbonate and polybutylene teraphtalate in a cable, each module containing one, two or four optical fibers. The external diameter of these modules is 1.4 mm.
Patent document FR 2 914 752, discloses a cable that has a longitudinal central cavity receiving a set of optical fiber micro modules arranged in a parallel manner, and a sheath surrounding the central cavity. A protection armor, e.g. steel strap, is arranged on an inner periphery of the sheath, and each micro module includes a maintaining sheath of an optical fiber surrounded by an external layer having friction coefficient higher than that of the maintaining sheath. It also discloses a method for extracting a micro module of an optical fiber telecommunication cable. This patent document describes parallel modules in a cable, each micro module containing 4 to 24 optical fibers. The external layer of the micro modules could be Polyamide.
Patent document US2005/0265673 discloses a communication cable buffer tube having a flexural modulus ranging from about 1.24*106 to 1.93*106 kPa (180 to 280 kpsi). Buffer tubes made of e.g. Polycarbonate, polyamide (such as nylon 12) and combinations thereof are also disclosed.
The Applicant of the present patent application, a subsidiary of Prysmian Group, operates an optical cable referenced as Retractanet© that comprises retractable fiber modules called PicoFlex© in which optical fiber bundles are embedded in a special soft hot melt. A layer of technical polymer such as polyamide is then extruded on the special hot melt layer. These modules own specific technical attributes regarding their thermal stability, low friction coefficient, tensile strength and strip ability, allowing the optical cable to be operational.
These modules are soft enough to be flexible and easy to handle, while at the same time being stiff enough to retract long distances within the cable and be pushed or blown through small micro-ducts as well.
However, there is a need for improving such an optical cable, in order for an operator to access more quickly the optical fibers within the modules and to extract quickly and on a long distance said fibers from the cable.
More generally, it would be desirable to improve the fiber access of fibers contained in retractable modules, while keeping sufficient strength of the module to withstand the pulling forces during module extraction from the cable.